Field assignment final

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Transcript of Field assignment final

  • 1.John Fors
    Professor Lawler
    GEL 104, Summer 2011
    July 10, 2011
    Middle Fork of The American RiverField Assignment

2. Content
Background & Method
Brief Geological History
River Canyon Geology
Gold Deposits
Rock Examples
Geological Features
Plant Examples
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3. Background and Research Methodology
In late June I visited an area in the canyon of the Middle Fork of the American River
The photos and rock samples included in this report are from this field trip
3D map images were prepared using Google Earth
Identification of rocks done using: Geology of the Sierra Nevada, by Mary Hill (2006)
Identification of plants done using: Trees and shrubs of California, by Stuart & Sawyer (2001)
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4. Site Location
Near Auburn, California
Entry through Drivers Flat Road, on dirt road down to bottom of river canyon
Coordinates 38.962362,-120.929775
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5. Deep Down in the River Canyon
Google Earth
View up the very deep canyon of Middle Fork of American River
Valley has been carved by the flow of the river for last several million years
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6. Quick Geological History and Overview
Sierra Nevada is a tilted fault block 400 miles long, with rugged east face, and sloping west face
West side has metamorphic rock formed by plate tectonics in Early Paleozoic to Late Jurassic (400-120 million years ago) with portions of ancient seafloor
Volcanic eruptions filled ancient valleys with lava and mudflows
Present river system formed by erosion during last 5 million years
(Lindstrom, 2000; North, 2006; North, 2007)
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7. Geology of Middle Fork River Canyon
Undulating steep mountains, elevation 1,600 5,600 feet
Foresthill Divide is a NE trending ridge system, separating North and Middle Forks of American River
River has cut steep canyons 1000 ft below top of Foresthill Divide
Significant surface erosion, especially on steep hill sides
Mean annual precipitation between 30-40 inches
Extremely low seismic activity
(North, 2006; North, 2007)
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8. Gold Deposits Around Foresthill Area
Streams flowing down western slopes carried Auriferous gravels
Auriferous gravel